Longitudinal slices of thickness ∼10 Mpc (i.e. four times the smoothing length) of the reconstructed (top for S/N = 4 and middle for S/N = 10) and original (bottom) optical depth contrast field τ/⟨τ⟩−1, where τ = −logF and F is transmitted flux. τ is taken as a proxy for the HI density. The original field is smoothed with a Gaussian kernel over 2.5 Mpc. Filaments extracted with DISPERSE are overplotted in grey and black. The black lines correspond to the 50% densest filaments. As noise in the spectra increases, the reconstruction shows lower contrast, and filaments are more randomly located.